Two forces are pushing on an object, one at 12 lbs of Force and one at 5.66 lbs of Force. The angle between them is 35° (each is 72.5 from horizontal, such that the forces make a v with the object in the center).

make a sketch
complete the parallogram with the resultant as the diagonal
consider the triangle with sides 12 and 5.66 with the contained angle of 145°, with the longest side representing the resultant
let that longest side be x
by cosine law
x^2 = 12^2 + 5.66^2 - 2(12)(5.66)cos 145°
..
..
x = 16.95... (total force on object)